  #include "csapp.h"
    int main(int argc,char **argv)
    {
    struct in_addr inaddr;
    uint32_t addr;
    char buf[MAXBUF];
    if(argc !=2){
    fprintf(stderr,"usage:%s<hex number>\n",argv[0]);
    exit(0);
    }
    sscanf(argv[1],"%x",&addr);
    inaddr.s_addr=htonl(addr);
    if(!inet_ntop(AF_INET,&inaddr,buf,MAXBUF))
    unix_error("inet_ntop");
    printf("%s\n",buf);
    exit(0);
    }
